1. Technical Field
This invention relates generally to a method and apparatus for rotationally indexing a workpiece for machining operations.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
It is known to rotationally index a workpiece to advantageously position the workpiece for machining operations to be carried out on the workpiece. It's also known for such rotational indexing to be carried out by an apparatus including a turntable or spindle supported on a housing for rotary indexing. Such an apparatus will typically include some type of turntable locking system that alternately releases and locks the turntable to rotationally index a workpiece carried by the turntable and hold the workpiece in desired indexed positions while a machining operation is carried out on the workpiece.
For example, U.S. Pat. No. 2,808,741 issued 8 Oct. 1957 to Bellmann and U.S. Pat. No. 3,667,305 issued 6 Jun. 1972 to Rasoira disclose rotary workpiece indexing apparatus that each include a turntable carried by a shaft and supported for rotary indexing on a housing, and a motor that's carried by the housing and is drivingly connected to the shaft to drive the shaft and turntable in rotation relative to the housing. The rotary workpiece indexing apparatus of the Bellmann and Rasoira patents also each include a turntable locking system that includes brakes positioned to secure the turntable against rotational motion relative to the housing by applying axially-directed braking force at least three respective locations spaced around the turntable. In each case the brakes each include an axially-oriented bolt whose head is received in a ring channel or keyway formed into and around a lower surface of the turntable, the bolts being spring-loaded to respective engaged positions where undersides of the bolt heads are brought to bear against annular engagement surfaces in the ring channel. Each brake further includes a bolt release linkage that moves the bolt out of its engaged position to release the turntable for rotation. The release linkage of the Bellmann patent is manually operated and the linkage of the Rasoira patent is hydraulically actuated.
U.S. Pat. No. 6,457,383 issued 1 Oct. 2002 to Kschier discloses a rotary workpiece indexing apparatus comprising a turntable supported for rotation on a housing and a turntable locking system that includes a spreader or pressure ring connected to the bolts. In response to the bolts being drawn axially by the linkages, the pressure ring spreads thin-walled ring segments of a ring-shaped brake shoe outward into engagement with inner walls of a concentric ring groove formed in an underside of the turntable.
For each of the above systems, the positioning of the linkages, bolts, and other braking system components beneath and/or within the turntables, and the interfaces between these components and the undersides of the turntables, requires a significant amount of space and reduces considerably the amount of metal and other structural material that could otherwise be included in or carried by the housing and table to provide additional dimensional stability and help support a workpiece against radial, axial, and torsional motion—especially in high-load machining operations such as high-tonnage broaching.